Fire engulfed a 24-floor housing block in central London in the early hours on Wednesday, killing at least 12 people and injuring 79 others in an inferno that trapped residents as they slept.

Flames raced through the high-rise Grenfell Tower block of apartments in the north Kensington area after taking hold around 1 am and witnesses reported some residents screaming for help from windows of upper floors and others trying to throw children to safety, reported Reuters.

More than 200 firefighters, backed up by 40 fire engines, fought for hours to try to bring the blaze, one of the biggest seen in central London in memory, under control, it stated.

The Metropolitan Police updating the death toll said 12 people had died and warned that the figure would almost certainly rise.

“In my 29 years of being a firefighter, I have never, ever seen anything of this scale,” Dany Cotton, commissioner of the London Fire Brigade, was quoted as saying by the New York Times.

By early afternoon, more than 250 firefighters from all over London were searching for victims and working to extinguish the remnants of the blaze, which was reported at 12:54 a.m. in Grenfell Tower, in the North Kensington area.

The fire was the latest tragedy in a country that has seen three deadly terrorist attacks, two in London and one in Manchester, since March.

The office of Prime Minister Theresa May said she was “deeply saddened” by the disaster and would convene a 4pm meeting to coordinate the government’s response, said the NYT report.

Constructed in 1974, Grenfell Tower has 24 stories, with 120 apartments across 20 residential floors; it is owned by the local government and managed by an outside company. A refurbishment was completed last year.

The cause of the fire was not immediately known, but a tenant group had complained for years that the management company was inattentive and that the building was at risk of a deadly fire, said the NYT report.

Forty fire trucks were involved in fighting the blaze, and more than 20 ambulances were sent to the scene. The London Ambulance Service said it had taken 64 patients to six hospitals, and that 10 others had gone on their own. Twenty were in critical condition.

Alison Evans, who lives near Grenfell Tower, woke to the sounds of sirens and helicopters and watched the fire engulf the building from a nearby street.

“It just kept burning and burning for hours and for hours there were still people at the top of the building screaming for help,” she said. “It was hell to watch. We were watching people dying. I can’t imagine how many people must have died in there,” Evans was quoted as saying.

Horrified witnesses told how they saw people jumping from windows as high as the 15th floor of a tower block as a huge fire engulfed the building, reported The Evening Standard.

Residents reportedly used bed sheets as makeshift ropes, while others are said to have jumped from their flats to escape the inferno as it tore through the building within minutes.

The London Fire Brigade confirmed there were "a number of fatalities" but could not confirm the total figure.

One witness, named only as Daniel, told the BBC: “Nobody could come out, they were trapped in there. They couldn't come down because the lift's the other side.

I’ve seen people jump… one at least, 10-15 floors up.”

Another witness described the scenes as horrifying as the flames engulfed the block from the second floor up “within seconds”.

“I couldn't believe my eyes. When I came out people in the tower block were waving their phones, screaming ‘help, help, help’”, another witness said. The whole tower is engulfed in flames.”

Whalid Kalan, 44, who lives in a nearby street, said: "I've never seen anything like it before, we live just 700 m away and the smoke and he dust covered all the cars there.

"It's just shock thinking about the children in the school nearby. We're worried that there is life lost," he told BBC.